Community Airborne Research Instrumentation (CARI) Group

CARI Projects Calendar

CARI Group members:

 

Overview

 

The recently formed CARI group is currently responsible for a number of aircraft trace gas instruments, including instrumentation which can be requested via the NSF/LAOF process, NSF/NCAR GV (HIAPER) instruments (two of those are part of the HAIS suite), and others. These instruments are:

 

CO: Two vacuum flourescence instruments (Aerolaser, one certified for GV)

CO2: Two infrared absorption carbon dioxide instruments (Li-Cor, one certified for GV)

H2O: Two TDL infrared absorption open-path water vapor instruments (MayComm Instruments, one certified for GV)

Fast-O3: "Inverse" chemiluminescence instrument (home built for GV - HAIS)

NOx, NOy: compact 2-channel chemiluminescence instrument / photolytic conversion /gold catalytic conversion (home built for GV)

NOx, NOy, O3: 4- channel chemiluminescence instrument / photolytic conversion /gold catalytic conversion (home built for various aircraft, not certified for GV)

PANs: Thermal dissociation Chemical Ionization Mass Spectrometer (built in collaboration with Georgia Tech)

VOC: TOGA fast GC-MS instrument measuring a variety of VOC (alkanes, alkenes, oxygeneates, aromatics, and others, about 40 compounds total) on a 2-min time scale (home built for GV - HAIS)

 

The group expects to take responsibility for one or more of the HAIS instruments after they have been delivered to EOL.

 

Summary of Activities for FY07:

Field Experiments and instrument preparation/improvements:

 

CARI participated in five field experiments in the last year. The TexAQS 2006 campaign, led by NOAA ESRL and funded by NOAA (http://www.esrl.noaa.gov/csd/2006/), the Pacific Dust Experiment (PACDEX; funded by NSF), the Airborne Carbon in the Mountains Experiment (ACME; funded by NSF), The Pacific Sulfur Experiment (PASE; funded by NSF), and the Tropical Composition, Cloud and Climate Coupling (TC4) experiment (led and funded by NASA).

 

The TexAQS 2006 experiment was flown on board the NOAA P-3 in September and October 2006. CARI participated with the PANs- CIGARette instrument. This effort is described separately under the "Megacities and the Effects of Urbanization" section. Final data was delivered to the data archive and data analysis and interpretation has begun. First results were presented at the TexAQS 2006 data workshop in Austin, TX, in August.

 

The Pacific Dust Experiment (PACDEX), April and May, 2007, tracked Asian plumes as they advected across the Pacific, characterizing the extent of transpacific transport of continental components including dust, black carbon and CO. A particular focus of PACDEX was characterization of cloud interactions with these plumes and airmass physical and composition changes resulting therefrom. Chemical, meteorological forecasts, as well as dust and CO satellite products enabled the investigators to predictably locate and sample the plumes in a quasi-Lagrangian manner. The CARI CO instrument was deployed on the NSF/NCAR G-V as a combustion tracer.

 

The Airborne Carbon in the Mountains Experiment (ACME-07), April 4-August 10, 2007, undertook a Lagrangian approach to quantify regional integrated carbon fluxes over the heterogeneous terrain of the Colorado Rocky Mountains. The 2007 airborne component of the Carbon in the Mountain Experiment (CME) helped constrain model flux estimates and extend inferences drawn from the CME network of continuously monitoring ground sites. The CARI group provided mission-critical measurements of CO and CO2 mixing ratios on the UW King Air platform. Improvements to the airborne CO2 instrument electronics and data acquisition system were implemented in preparation for the ACME-07 campaign. Improved noise specifications and reliability of operation were observed.

 

CARI configured the 2-channel NO-NOy instrument for flight in a pallet on the WB-57F for participation in TC4.  This proved to be a valuable testing opportunity and has led to design changes that will be incorporated before the instrument is flown again.

 

The Pacific Atmospheric Sulfur Experiment (PASE), August 1 - September 8, 2007, studied the chemistry and dynamics of sulfur species in the clean marine boundary layer, with a special emphasis on the impact of these species and their oxidation products on local aerosol physics, including CCN. The CARI group provided CO, fast-Ozone and water vapor mixing ratio measurements on the NSF/NCAR C-130. The fast-response ozone and water vapor measurements additionally will support estimations of boundary layer entrainment rates.

 

Data Analysis and interpretation

MIRAGE

 

TOGA volatile organics measurements were combined with whole air sample analyses from the University of California, Irvine to obtain an understanding of the distribution of non-methane hydrocarbons (NMHCs), oxygenated volatile organic compounds (OVOCs), halogenated compounds and acetonitrile, an important tracer for biomass burning in the MCMA and areas of Mexico away from the city. Above the MCMA, the most abundant VOC measured was methanol followed by propane, formaldehyde, acetone, and acetaldehyde. The most reactive VOCs in terms of OH-reactivity were acetaldehyde, formaldehyde, propanal and methanol (see figure 1). We speculate that short-lived (highly reactive) low molecular weight VOC species provide the primary driving force for ozone formation in Mexico City and that in the MCMA the lifetimes are short enough so that there is little carry over from day to day. Primary emissions of ethylene, propylene, formaldehyde, and acetaldehyde (and secondary formaldehyde and acetaldehyde production from the oxidation of ethylene and propylene) are the important low molecular weight OVOCs. This work suggests that there is potential for significant reductions in oxidant formation from efforts to reduce the emissions of these few species.

 

The reactive nitrogen measurements made on the C-130 were combined to investigate the budget and speciation of NOy in the Mexico City (MC) plume. Figure 2 shows the evolution of NOy partitioning in the outflow from Mexico City compared to New York City (NYC, from ICARTT 2004). It is apparent that in the relatively low-altitude, high humidity and temperature environment downwind of NYC the PAN reservoir is relatively small and almost all of the emitted NOx is converted to HNO3 within one day. Ozone production further downwind will therefore be limited by the availability of NOx. The MC outflow, on the other hand, occurs at higher altitudes (because of the elevation of the city combined with a very high PBL up to 5 km asl) and therefore lower temperatures. PANs comprise about half of the NOy after 2 days of transport and through slow decomposition maintain a NOx level which is sufficient to continue to produce ozone for several days downwind of the city.

 

As part of further study of the evolution of NOy partitioning, the sampling of the aerosol component of NOy needs to be better understood.  The flow around the NOy inlet is being modeled (Fluent software), along with the aspiration efficiency of NOy-containing aerosols for a quantitative evaluation of the aerosol component of the NOy measurement.  This work will involve a collaboration with investigators (Jimenez et al., U of Colorado) who operated the Aerosol Mass Spectrometer (AMS) on the C130 during MIRAGE.  As a first step in this analysis, the flow field around the NOy inlet has been modeled (Figure 3).

 

 

 

 

Figure 1: distribution of VOC and reactivity in Mexico City

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 2: NOy partitioning and ozone production downwind of Mexico City (top) New York City (bottom, from ICART 2004)

 

Fig. 3: Velocity vectors for 200 m/s aircraft speed over inlet showing recirculation.

 

INTEX-B

 

TOGA VOC measurements made on board the C-130 during INTEX show strong evidence of oceanic uptake of several oxygenated VOC. Figure 4 shows a composite of all altitude profiles of acetone, methanol and CO flown over the ocean. Acetone and methanol show clear decreases in the surface layers while CO does not. The MOZART model does not capture this observed decease because ocean uptake is not included in the model (methanol is underestimated because the sources of methanol are not well known at this time and strongly underestimated in global models), while the profile of CO is well reproduced. Oceanic uptake rates of 4.7 and 3.3 µmole m2 day-1 can be derived for acetone and methanol, respectively.

The previously reported oceanic uptake rate for acetonitrile (deGouw et al.) was included in the MOZART model and the altitude profiles observed by the TOGA instrument were well reproduced with the model.